[css-ruby] Define proper box model for merged annotations

Author: frivoal

css-ruby-1/Overview.bs

@@ -1193,8 +1193,9 @@ Sharing Annotation Space: the 'ruby-merge' property</h3>
 
 		<dt><dfn>merge</dfn>
 		<dd>
-			All [=ruby annotation boxes=] within the same [=ruby segment=] on the same line are concatenated,
-			and laid out as if their contents belonged to a single [=ruby annotation box=]
+			All [=ruby annotation boxes=] within the same [=ruby segment=] on the same line are concatenated
+			as [=inline boxes=] within their [=annotation container=],
+			and laid out in a single anonymous [=ruby annotation box=]
 			spanning all their associated [=ruby base boxes=].
 			This style renders similar to “group ruby” in [[JLREQ]],
 			except that [=ruby annotations=] are kept together with their respective [=ruby bases=] when breaking lines.